- Add a new CourseEnrollmentCelebration model, which ties a
course enrollment to some booleans about progress celebrations
- Add serialization of the new model to the existing courseware_api
app's existing course info view
- Add new API in courseware_api to update a celebration model
Change from specifying a retired username/email format to specifying
a retired username prefix and a retired email prefix/domain,
preventing possible config errors due to unexpected/bad formats.